Many states are considering what climate change is going to mean for their infrastructure, and Hawaii says their estimated price tag is $15 billion. According to Ed Sniffen, Hawaii’s Department of Transportation (HDOT) deputy director for highways, the state is estimating it will cost $15 billion to raise, push back, or relocate highways to address concerns over rising seas levels because of climate change. Initial estimates indicate about 15 percent of all HDOT highways will be susceptible to rising sea levels. On average, the state is expecting costs of $7.5 million for every mile of affected highway and $40 million for every mile of affected bridge. These estimates are the result of an effort by the state to defend its highway system against future climate change impacts, some which have already become apparent.

Unfortunately, highway damage due to rising sea levels is not new to Hawaii residents. In 2016, HDOT repaired the vital Kamehameha Highway after high surfs caused enough damage to close lanes of traffic. HDOT has already acknowledged that previous highway repairs due to sea level rise are only a short-term strategy, “It’s something that’s coming, so we’ve got to address it,” says Sniffen. Having previously fortified highways by building expensive walls, HDOT has turned to using less expensive items such as boulders to stabilize eroding highways. Sniffen said that building expensive walls was “millions of dollars that we’re putting in an area that we’re not going to be in very soon.”

The Hawaii Climate Change Mitigation and Adaptation Commission, tasked with planning for sea level rise adaptation, predicts up to 3.2 feet of global sea level rise by year 2100. The commission also predicts that approximately 38 miles of road would be chronically flooded across the state with the anticipated rise in sea level. Aside from flooding, additional roads would likely be negatively affected structurally by more erosion due to the high waters.

One challenge that the state will be facing is prioritizing which highways to modify first. Sniffen described how a road’s priority level depends on factors such as expense, adjacent residents, traffic levels, and economic activity. Other factors such as highway design become a challenge as well. “Elevating the highway on Oahu’s Windward side would probably involve raising the road as high as 9 feet, but that would also be too steep of an incline for residents on the mauka [inland] side of the road to access it,” says Sniffen. A potential alternative could include relocating the highway inland and through the Koolau mountain range.

Challenges such as these faced by Hawaii are predicted to become more evident as the impacts of climate change unfold. Credit HDOT and the Hawaii’s Climate Change Mitigation and Adaptation Commission for beginning to plan for these outcomes.